A magnetic disk drive storage device typically comprises one or more thin film magnetic disks, each having at least one data recording surface including a plurality of concentric tracks of magnetically stored data, a spindle motor and spindle motor controller for supporting and rotating the disk(s) at a selected RPM, at least one read/write transducer or “head” per recording surface formed on a slider for reading information from and writing information to the recording surface, a data channel for processing the data read/written, a positionable actuator assembly for supporting the transducer in close proximity to a desired data track, and a servo system for controlling movement of the actuator assembly to position the transducer(s) over the desired track(s).
Each slider is attached on one surface to an actuator arm via a flexible suspension and includes on an opposite side an air bearing surface (ABS) of a desired configuration to provide favorable fly height characteristics. As the disk rotates, an air flow enters the slider's leading edge and flows in the direction of its trailing edge. The air flow generates a positive pressure on the ABS, lifting the slider above the recording surface. The slider is maintained at a nominal fly height over the recording surface by a cushion of air.
To avoid the problems associated with contact during start/stop of the disk, some disk drive designs employ “load/unload” technology. According to this design, a ramp is provided for each slider/suspension assembly at the inner or outer diameter of the disk where the slider is “parked” while the spindle motor is powered down. During normal operation, the disk speed is allowed to reach a selected RPM (which may be below the normal operating RPM) before the head is “loaded” onto the disk from the ramp on the air cushion generated by the disk's rotation. In this manner, the slider flies over the disk without significant contact with the disk surface, eliminating contact start/stop wear. The load/unload ramp structure is generally made of plastic which can be injection molded into complex ramp structures.
With lower fly heights between the transducer head and the magnetic disk during operation of the disk drive, there is an increasing rate of intermittent contacts between the head and the disk resulting in damage to the disk surface. Although the disk is coated with lubricant during manufacture to protect it from such intermittent contact, during operation of the drive, the lubricant is depleted from the surface of the disk. Because of the problems associated with lubricant spin-off from the disk, a vapor phase lubricant reservoir system has been disclosed as a means for continuously maintaining a uniform lubricant film on the disk as described in U.S. Pat. No. 4,789,913 issued Dec. 6, 1988, which is herein incorporated by reference. The patent describes a method for lubricating the disk during operation of the drive. This method of lubrication continuously maintains the lubricant film on the disk drive during operation of the drive. U.S. Pat. No. 6,580,585, issued on Jun. 17, 2003 and also incorporated by reference, discloses a system using a porous lubricant reservoir positioned near the heads parked on the ramp. Lubricant having a high vapor pressure is disposed in the reservoir. During shutdown of the drive when the heads are parked on the ramps, the lubricant from the reservoirs provides a thin adsorbate film of lubricant on the heads. This system minimizes the vapor-phase concentration gradient between the reservoir unit and the nearest head so as to maintain a well-controlled lubricant film on the surface of the head. The lubricant reservoirs can also be positioned on the body of the load/unload structure near the heads parked on the ramp.
To achieve the aforementioned low fly heights, and corresponding shorter magnetic spacing, the slider is designed to be in full contact with the disk at initial stages in order to wear off typically 1-10 nm from the trailing edge of the ABS surface. More particularly, when the drive is started for the very first time, the slider starts in contact with the disk and is burnished (i.e., worn off) so that the slider trailing edge self-adjusts to the correct height and eventually either flies above the disk at a very low fly height or drags on the disk in contact with low friction and spacing modulation. A second advantage is that all or part of the carbon overcoat added to the slider to protect the slider from corrosion during manufacturing is removed. By removing the carbon overcoat, a gain of several nanometers (˜1-5 nm) in the magnetic spacing can be achieved. A third advantage is that the standard deviation on the magnetic spacing is dramatically reduced compared to a traditional flying slider because each slider self-adjusts to the same final magnetic spacing, independent of parameters such as suspension gram load, pitch static attitude (PSA), or other manufacturing imposed variations.
However, as mentioned above, lubricant is placed on the disk prior to installing the disks into a drive to protect the slider and disk. The lubrication of the disk, by design, dramatically slows the wear process. A typical burnishing cycle on a lubricated disk can take 10-40 minutes on current disk substrates. While this may seem like a relatively short amount of time, one should keep in mind that every drive on the manufacturing line must be run for that long to burnish the slider to the final design point before servo data can be written. Thus, it would be desirable to reduce the burnishing time required during disk drive manufacture.
Another problem addressed in this disclosure is the badly controlled burnish process observed when trying to burnish these sliders on fully lubricated standard production disks. As mentioned above, finished hard disks are covered with a layer of lubricant (a perfluoroether polymer) prior to installation in the drive. To ensure replenishment capabilities, a fraction of this lubricant is not bonded to the disk surface. It has been observed that interaction between the slider trailing edge and the free lubricant can lead to severe instabilities, causing the slider to oscillate at its second pitch natural frequency (around 300 kHz for currently tested sliders) with an amplitude of more then 5 nm. This is a serious problem for disk reliability purposes, and more important it can cause incomplete and/or inconsistent burnishing of the slider. Thus it would also be desirable to reduce lubricant induced slider oscillation by avoiding lubricant transfer between the disk and the slider.